The present invention relates to an improved means for preventing water hammer in a fluid-feeding system utilizing a jet mixer therein.
It is well known to utilize a jet mixer to add or mix a gaseous or aqueous material into a fluid-feeding system flowing with a predetermined flow rate to process the inflow fluid, for example, as an inline steam heater for heating and hot water service, means for liquid temperature control or automatic heating fluid temperature control, or for chemical processing as disclosed in British Patent Specification No. 1,156,820, etc.
In general, a jet mixer comprises, as shown in FIG. 1, a casing 1 having an inlet 2 and an outlet 3 for a fluid-feeding system, a supply port 4 for a gaseous or aqueous material to be mixed into the fluid-feeding system, and a venturi-type jet tube 5 interposed between and fixed to the inlet 2 and the outlet 3, having at its periphery a plurality of jets 7 which are oriented at an acute angle to the direction of flow of the fluid-feeding system. The jet tube 5 has a through passage 6 (see FIG. 2) so configured to have a decreasing cross-sectional area, progressively, from the inlet 2 toward an intermediate portion and then increasing, progressively, toward the outlet 3. The connection of the jet tube 5 to the casing 1 is effected by means of, for example, thread-engagement 8 at one end thereof and fit-engagement through a packing 9 at the other end. A drain plug 11 is also provided.
With the jet mixer having aforementioned arrangement installed in the fluid-feeding system, the gaseous or aqueous material (fluid) which is intended to be mixed into the fluid-feeding system is introduced through the supply port 4 into the chamber defined between the jet tube 5 and the inner wall of the casing 1, and then is sucked through the plurality of jets 7 and mixed with the fluid passing through the venturi-shaped passage 6.
On this occasion, a water hammer is liable to occur in the fluid-feeding system due to abrupt changes in the flow rate and the density of the fluid in the system, caused by passage of the mixing fluid through the small jets 7, resulting in vibration or noise.
In order to avoid the above phenomenon, a proposal has been made in the prior art, as disclosed in Japanese Utility Model Publication No. 31468/1977, in which a cross-woven or knitted screen consisting of fibrous metal filaments made of, for example, stainless steel is padded in the chamber defined by the jet tube and the inner wall of the casing of the jet mixer (see reference numeral 10 in FIG. 2).
With aforementioned arrangement, the drawbacks such as noise and vibration in the fluid-feeding system caused by such water hammer have been substantially remedied, due to a decelerating effect of the screen against the inflowing mixing fluid. However, in practice, some further problems are left.
That is, the fibrous metal filaments of the cross woven or knitted screen used in the above example are (1) apt to be deteriorated in their ability as a screen due to accumulation of rust, dirt and the like therebetween, and (2) liable to break into small pieces within the casing and flow into the fluid-feeding system, causing the components of the system to be damaged, or clogging the screen and so on, and in particular, in the case of an edible fluid, those small pieces may have fatal affects.